1. Technical Field
This invention relates generally to methods for producing films, and more particularly to methods for producing thin films in superconducting circuits.
2. Background Art
The phenomenon of superconductivity was discovered by K. H. Onnes in 1911 when he demonstrated that the electrical resistance of mercury drops to zero when it is cooled to approximately 4 Kelvins (K) above absolute zero temperature. For many years the phenomenon remained a scientific curiosity, with few practical uses.
Theoretically, superconductivity has many potential uses. For example, superconducting power lines could save a great deal of energy would otherwise be dissipated during transmission. Small and extremely powerful superconducting magnets, generators, and motors could be built. Superconducting devices known as Josephson junctions are extremely fast electronic switches having very low power consumption. In fact, the potential uses for superconducting materials are so many and varied, that an attempt make a comprehensive list of possible applications is almost an exercise in futility.
Despite the potential benefits of superconducting devices and structures, in the past they were seldom found outside of research laboratories because it was too expensive to cool most materials to their superconducting transition temperature T.sub.c. This was due to the fact that, prior to early 1987, all known superconductor materials had a transition temperature within a few dozen degrees Kelvin of absolute zero, requiring the use of expensive liquid helium cooling systems.
On Mar. 2, 1987, M. K. Wu et al. published a paper entitled "Superconductivity at 93 K in a New Mixed-Phase Y-Ba-Cu-O Compound System at Ambient Pressure" in Physical Review Letters, Volume 58, Number 9. This announcement caused considerable excitement in the scientific and business communities because, for the first time, a superconductor material had been discovered which could use liquid nitrogen as a coolant. Since liquid nitrogen cooling systems are at least an order of magnitude less expensive than liquid helium cooling systems, many applications for superconductors suddenly became practical after Wu et al.'s discovery.
One of the more promising uses for this new material is the aforementioned Josephson junction devices. Because Josephson junction devices can switch on-and-off extremely quickly, they can improve the performance of digital circuitry by several orders of magnitude. For example, Josephson junction devices can be used in picosecond sampler circuits and in ultra-fast supercomputers.
A problem with making Josephson junction devices with the new YBaCuO material is that it is difficult to deposit and pattern. More often than not, attempts at etching thin films of YBaCuO by using conventional photolithographic techniques have resulted in the destruction of its superconducting properties.